1. Field of the Invention
The present invention relates to a control apparatus that controls a hybrid type outboard motor equipped with an electric motor as a drive source to rotate a propeller and an engine which performs exhaust in the water, and a running support system and a marine vessel using such a control apparatus.
2. Description of Related Art
An outboard motor is one type of propulsion systems for marine vessels that provides a propulsive force to a marine vessel. In the outboard motor, a motor that generates a drive force to rotate a propeller is disposed outboard.
In addition, a so-called hybrid type motor equipped with both an engine and an electric motor has been proposed. A hybrid system disclosed in Japanese Unexamined Patent Publication No. 2004-257294 is devised so that both of an engine and an electric motor are driven or only one of the engine and the electric motor is driven, and the drive force thereof causes a propeller to rotate. Furthermore, in the hybrid system, where both the engine and the electric motor are driven, the output of the electric motor is regulated based on the operating speed and operating time of an operation lever operated for steering, and an opening degree of a throttle and rotation fluctuation time of the engine.
In a marine vessel including an outboard motor that uses a hybrid motor (herein after called a “hybrid type outboard motor”), the propeller is rotated only by a drive force of an electric motor, for example, at very low running speeds. This is because a required propulsive force is so low that it cannot be properly output unless the rotational speed of the engine is set to be less than the idling rotational speed of the engine. On the other hand, as the running speed of a marine vessel exceeds a predetermined value, the drive force of the engine is transmitted to the propeller since the rotational speed of the engine corresponding to a required propulsive force exceeds the idling rotational speed.
In a conventional outboard motor, where the engine is driven, an exhaust gas is exhausted in the water through an in-water exhaust port provided at the boss part of the propeller. This is called “in-water exhaust.”
FIG. 1A is a conceptual view describing the in-water exhaust, which shows a forward running state of a marine vessel. FIG. 1B is a conceptual view describing the in-water exhaust, which shows a reverse running state of a marine vessel. In a state in which an operator operates the operating lever in the forward direction, and the marine vessel runs forward, as shown in FIG. 1A, the propeller is rotated in the direction along which water is pushed out astern. Therefore, bubbles of exhaust gas exhausted in the water move backwards. However, as the marine vessel moves backward in response to the operator's operation of the operating lever in the reverse (backward) direction, the propeller rotates in water containing bubbles as a result of the exhaust (see FIG. 1B). At this time, “bubble entrainment” occurs, by which the propeller drags or entrains bubbles. Therefore, since the water amount pushed out by the propeller is substantially reduced, the propulsion efficiency is reduced accordingly. That is, it becomes impossible to obtain a propulsive force corresponding to the rotational speed of the propeller. Furthermore, since the exhaust amount from the engine is increased in accordance with an increase in the rotational speed of the propeller, the bubble entrainment is substantially increased in response thereto. Accordingly, the higher the rotational speed becomes, the greater the degree of reduced propulsive force resulting from the bubble entrainment becomes.
On the other hand, since no in-water exhaust occurs when the propeller is driven by only an electric motor with the engine stopped, the propulsive force is not reduced due to bubble entrainment. For this reason, in a hybrid type outboard motor, when moving a marine vessel backward, at the time of shifting from a state in which the propeller is rotated only by an electric motor to a state in which the propeller is rotated by the engine, there is a concern that the propulsive force may become discontinuous. Therefore, there is a possibility that an operator and other passengers will experience uncomfortable feelings.
In particular, since a marine vessel runs at a low speed when arriving at or leaving a shore or trolling, the state of the hybrid type outboard motor is frequently changed between a state in which the propeller is driven only by an electric motor and a state in which a drive force of an engine is transmitted to the propeller. Thus, uncomfortable feelings experienced by passengers due to discontinuance of the propulsive force are increased.